The invention relates to an embolic protection device.
The term xe2x80x9cSTROKExe2x80x9d is used to describe a medical event whereby blood supply to the brain or specific areas of the brain is restricted or blocked to the extent that the supply is inadequate to provide the required flow of oxygenated blood to maintain function. The brain will be impaired either temporarily or permanently, with the patient experiencing a loss of function such as sight, speech or control of limbs. There are two distinct types of stroke, haemorrhagic and embolic. This invention addresses embolic stroke.
Medical literature describes caroitid artery disease as a significant source of embolic material. Typically, an atherosclerotic plaque builds up in the carotid arteries. The nature of the plaque varies considerably, but in a significant number of cases pieces of the plaque can break away and flow distally and block bloodflow to specific areas of the brain and cause neurological impairment. Treatment of the disease is classically by way of surgical carotid endarterectomy whereby, the carotid artery is cut and the plaque is physically removed from the vessel. The procedure has broad acceptance with neurological complication rates quoted as being low, somewhere in the order of 6% although claims vary widely on this.
Not all patients are candidates for surgery. A number of reasons may exist such that the patients could not tolerate surgical intervention. In these cases and an increasing number of candidates that are surgical candidates are being treated using transcatheter techniques. In this case, the evolving approach uses devices inserted in the femoral artery and manipulated to the site of the stenosis. A balloon angioplasty catheter is inflated to open the artery and an intravascular stent is sometimes deployed at the site of the stenosis. The action of these devices as with surgery can dislodge embolic material which will flow with the arterial blood and if large enough, eventually block a blood vessel and cause a stroke.
It is known to permanently implant a filter in human vasculature to catch embolic material. It is also known to use a removable filter for this purpose. Such removable filters typically comprise umbrella type filters comprising a filter membrane supported on a collapsible frame on a guidewire for movement of the filter membrane between a collapsed position against the guidewire and a laterally extending position occluding a vessel. Examples of such filters are shown in U.S. Pat. No. 4,723,549, No. 5,053,008, No. 5,108,419, WO97/17100 and WO 98/33443. Various deployment and/or collapsing arrangements are provided for the umbrella filter. However, as the filter collapses, the captured embolic material tends to be squeezed outwardly towards an open end of the filter and pieces of embolic material may escape from the filter with potentially catastrophic results. More usually, the filter umbrella is collapsed against the guidewire before removal through a catheter or the like. Again, as the filter membrane is collapsed, it will tend to squeeze out the embolic material. Further, the umbrella filter is generally fixed to the guidewire and any inadvertent movement of the guidewire during an interventional procedure can dislodge the filter.
The insertion of such known filters in the human vasculature which comprises very small diameter blood vessels may result in inappropriate haemodynamics which can exacerbate damage to the flowing blood and may result in haemolysis.
This invention is therefore directed towards providing an embolic protection device which will overcome these major problems.
According to the invention there is provided a collapsible filter element for a transcatheter embolic protection device, the filter element comprising:
a collapsible filter body which is movable between a collapsed stored position for movement through a vascular system and an expanded position for extension across a blood vessel such that blood passing through the blood vessel is delivered through the filter element;
a proximal inlet portion of the filter body having one or more inlet openings sized to allow blood and embolic material enter the filter body;
a distal outlet portion of the filter body having a plurality of outlet openings sized to allow through-passage of blood, but to retain embolic material within the filter body;
the distal outlet portion of the filter body in the region of the outlet openings having means for reducing shear stress on blood passing through the outlet openings.
In a preferred embodiment of the invention the shear stress reducing means includes lead-in radiussed portions of the filter body leading to the outlet holes.
In a particular embodiment of the invention the shear stress reducing means includes lead-out radiussed portions of the filter body leading from the outlet holes.
Most preferably the outlet holes are generally circular.
In another preferred embodiment of the invention the proximal inlet portion of the filter body in the region of the inlet openings has means for reducing shear stress on blood passing through the inlet openings. Preferably the shear stress reducing means includes lead-in radiussed portions of the filter body leading to the inlet holes. Ideally, the shear stress reducing means includes lead-out raduissed portions of the filter body leading from the inlet holes.
In a particularly preferred embodiment the filter is of a polymeric material. Preferably the filter body defines a three dimensional matrix. Most preferably, the filter body is of a resilient elastomeric material. The filter body may be of a polyurethane elastomer. Most preferably the filter body is of a polycarbonate urethane material.
In an especially preferred embodiment of the invention the filter body is covered with a hydrophilic coating, the openings being provided in the coating.
Preferably the filter is of a polymeric material and the raduissed portions are formed by solvent polishing of the polymeric material.
In a preferred embodiment the porosity of the distal portion of the filter body decreases towards the distal end of the filter. Ideally, the overall porosity of the distal portion of the filter element is from 5% to 40%. Preferably the overall porosity of the distal portion of the filter element is form 8% to 21%.
In a preferred embodiment in the transverse cross sectional areas at longitudinally spaced-apart locations of the distal portion are substantially the same.
Preferably the distal portion is of generally conical shape having a radial dimension which decreases towards a distal end of the filter element.
In one embodiment the distal portion includes a blind section adjacent to the distal end of the filter element. Preferably the blind portion extends longitudinally for at least 5% of the length of the distal portion, ideally for less than 30% of the length of the distal portion.
In a preferred arrangement the number of outlet holes increases towards an outer edge of the distal outlet portion of the filter body.
Most preferably there are between 200 and 1000 outlet openings with an average diameter of between 50 and 200 microns. Ideally, there are between 200 and 300 outlet openings with an average diameter of approximately 150 microns. There may be at least 200 outlet openings with an average diameter of no more than 200 microns.
Preferably there are less than 1000 openings with an average diameter of at least 50 microns.
In a particularly preferred embodiment the openings are sized such that shear stress imparted to blood flowing through the filter body at physiological flow rates is less than 800 Pa, most preferably less than about 400 Pa and ideally less than about 200 Pa.
The openings are ideally generally circular openings.
In a preferred embodiment said filter body, when in a deployed configuration includes a generally cylindrical intermediate section between said proximal and distal portions. The filter body is generally tapered when in a deployed configuration. Preferably said distal section of said filter body comprises at least a portion of the filter element. Ideally said intermediate section of said filter body comprises at least a portion of the filter element.
In a preferred embodiment the intermediate section of said filter body includes a circumferential groove.
In a particularly preferred embodiment said filter body, when in a deployed configuration is defined by a generally elongated shape, having an intermediate section with an axial dimension and a transverse dimension, the ratio of the axial dimension to the transverse dimension being at least 0.5, ideally at least 1.0.
In one embodiment of the invention the filter body includes a guidewire lumen extending co-axially of a longitudinal axis of the filter body.
In another aspect the invention provides a collapsible filter element for a transcatheter embolic protection device, the filter element comprising:
a collapsible filter body which is movable between a collapsed stored position for movement through a vascular system and an expanded position for extension across a blood vessel such that blood passing through the blood vessel is delivered through the filter element, the filter body having a proximal end, a longitudinal axis and a distal end;
a proximal inlet portion of the filter body having one or more inlet openings sized to allow blood and embolic material enter the filter body;
a distal outlet portion of the filter body having a plurality of outlet openings sized to allow through-passage of blood, but to retain embolic material within the filter body;
the porosity of the distal portion of the filter body decreasing towards the distal end of the filter.
In a further aspect the invention provides a collapsible filter element for a transcatheter embolic protection device, the filter element comprising:
a collapsible filter body which is movable between a collapsed stored position for movement through a vascular system and an expanded position for extension across a blood vessel such that blood passing through the blood vessel is delivered through the filter element;
a proximal inlet portion of the filter body having one or more inlet openings sized to allow blood and embolic material enter the filter body;
a distal outlet portion of the filter body having a plurality of outlet openings sized to allow through-passage of blood, but to retain embolic material within the filter body;
the filter body comprising a membrane of polymeric material;
wherein there are between 200 and 1000 outlet openings with an average diameter of between 50 and 200 microns.
The invention also provides a collapsible filter element for a transcatheter embolic protection device, the filter element comprising:
a collapsible filter body which is movable between a collapsed stored position for movement through a vascular system and an expanded position for extension across a blood vessel such that blood passing through the blood vessel is delivered through the filter element;
a proximal inlet portion of the filter body having one or more inlet openings sized to allow blood and embolic material enter the filter body;
a distal outlet portion of the filter body having a plurality of outlet openings sized to allow through-passage of blood, but to retain embolic material within the filter body;
the filter body comprising a membrane of polymeric material;
wherein the openings are sized such that shear stress imparted to blood flowing through the filter body at physiological flow rates is less than 800 Pa, preferably less than about 400 Pa.
In a further aspect the invention provides a collapsible filter element for a transcatheter embolic protection device, the filter element comprising:
a collapsible filter body which is movable between a collapsed stored position for movement through a vascular system and an expanded position for extension across a blood vessel such that blood passing through the blood vessel is delivered through the filter element;
the filter body having a longitudinal axis a proximal inlet portion, a distal outlet portion and an intermediate section extending between the proximal portion and the distal portion;
a proximal inlet portion of the filter body having one or more inlet openings sized to allow blood and embolic material enter the filter body;
a distal outlet portion of the filter body having a plurality of outlet openings sized to allow through-passage of blood, but to retain embolic material within the filter body;
the filter body having a guidewire lumen co-axial with the longitudinal axis;
wherein in a deployed configuration the intermediate section is generally cylindrical with an axial dimension and a transverse dimension, the ratio of the axial dimension to the transverse dimension being at least 0.5, preferably at least 1.0.
In yet another aspect the invention provides a transcatheter embolic protection device including:
a delivery system comprising:
a tubular member having a longitudinal axis, distal and proximal portions, said distal portion of the tubular member being removably advanceable into the vasculature of a patient;
a medical guidewire longitudinally axially movable in said tubular member and having distal and proximal portions;
and a filter element of any aspect of the invention the filter body having;
a first collapsed, insertion and withdrawal configuration an a second expanded, deployed configuration;
a proximal inlet section and a distal outlet section, said proximal inlet section including inlet openings which are operable to admit body fluid when the filter body is in the second expanded configuration;
a plurality of outlet openings disposed on at least a portion of the filter element adjacent to the distal outlet section;
wherein said filter body is moved between said first and second configurations by displacement of said delivery system.
Preferably the filter body has a collapsible filter frame operably coupled thereto. Said frame may comprise a plurality of support arms having proximal and distal ends. Preferably the arms are formed of an elastic shape memory material.
In a preferred embodiment said frame is constructed such that filter body is biased toward said second, deployed configuration.
In one embodiment of the invention said inlet openings are defined at least partially by said arms. Preferably proximal portions of said arms extend generally outwardly and distally from said guidewire when said filter body is in said second, deployed configuration.
In one embodiment distal portions of said arms extend generally outwardly and proximally from said guidewire when said filter body is in said second, deployed configuration.
Preferably the distal portion of the tubular member further includes a pod for receiving therein the filter body when in said first, collapsed configuration. Preferably said filter body is urged into said first, collapsed configuration by said pod when the guidewire is moved proximally.
In one embodiment said guidewire is solid.
In one arrangement said filter body comprises a sleeve slidably disposed on said guidewire. The device may further comprise stops for limiting the range of longitudinal movement of the sleeve on said guidewire. The sleeve may comprise a guidewire member distal to the filter body tapering distally.